The present invention relates to a method and system for transmitting an MPEG (Moving Picture Experts Group) image by use of the Internet Protocol (hereinafter referred to as IP). More particularly, the present invention relates to a network connection method using a transmission system conversion equipment for performing a rapid processing for conversion between an MPEG transport protocol and the Internet Protocol and a method for encapsulation of MPEG data to be transmitted. Also, the present invention relates to a method/equipment in which the conversion between an IP address and the PID (Packet Identifier) value of a TS (Transport Stream) packet is performed when a video signal transmitted using the Internet Protocol (IP) is to be transmitted by use of the H.222.0 system and a video transmission system which uses such a method/equipment.
As an international standard for a system for transmitting a video signal in a digitally coded form, xe2x80x9cGENERIC CODING OF MOVING PICTURES AND ASSOCIATED AUDIO: SYSTEMSxe2x80x9d has been prescribed as ISO(International Organization for Standard)/IEC(International Electrotechnical Commission) 13818-1, ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) H.222.0 Recommendation. This international standard for MPEG system (hereinafter referred to as H.222.0) has prescribed a standard for transmitting a video signal compressed on the basis of an MPEG system. Therein, two kinds of formats have been prescribed. One is a program stream (hereinafter abbreviated to PS) format supposing the transmission from a storage medium or the like for which the generation of bit error is relatively less. The other is a transport stream (hereinafter abbreviated to TS) format supposing a communication network for which the generation of transmission bit error is forecast.
Since the present invention is directed to a code conversion system when a compressed or coded video signal is to be transmitted in a TS format, brief description will now be made of the prior art of a video transmission system based on the TS format. In an MPEG system the object of which is the coding and transmission of video and audio signals, an inputted video signal such as a television signal is digitized and the obtained digital signal is subjected to data compression by use of techniques including discrete cosine conversion, variable-length coding, and so forth. Though techniques used in conjunction with an audio signal are different from those in the case of the video signal, the audio signal is compressed by removing redundant data after digitization. The compressed signal is termed an elementary stream (hereinafter abbreviated to ES) and is data which forms an elementary part of the video/audio signal in conformity with the term. In the MPEG, this video/audio data is represented using the term of (bit) stream.
In a cable television or community antenna television (CATV), satellite communication network, asynchronous transfer mode transmission network (hereinafter abbreviated to ATM network) or the like in which an MPEG video signal is transmitted, it is supposed that the generation of bit error at the time of data transmission is relatively frequent. Therefore, an elementary stream (ES) is transmitted in a form partitioned into small packets in order to narrow a range over which a trouble caused by transmission error extends. The packetized elementary stream (hereinafter abbreviated to PES) has a format in which header information called PES header is added to ES. In the transmission in the communication network exemplified above, PES is transmitted with a form further partitioned into smaller 188-byte packets called transport stream (TS) packets. As shown in FIG. 13, the TS packet includes a 4-byte header and a 184-byte payload for storing data. FIG. 14 shows the structure of the header of the TS packet. The TS header is composed of a 1-byte synchronization byte (0x47) 133, a flag 134 representative of the attribute of the TS packet (the explanation of the contents of the flag will be omitted since they are not important to the present invention), 13-bit packet identifiers (hereinafter abbreviated to PID) 135 and 136, a scramble control identifier 137, an adaptation field identifier 138, and a 4-bit cyclic counter 139 used for checking the continuity of the packet. In the transport stream, a field called adaptation field can be transmitted prior to a data field which is called payload and is used for storing video data. A program clock reference (hereinafter abbreviated to PCR) aiming at the clock synchronization of the system and private data can be stored in the adaptation field. It is prescribed that when the adaptation field is transmitted using the TS packet, the existence of the adaptation field should be designated by an adaptation field identifier in the TS header.
Though the MPEG system is a system developed corresponding to CATV or digital satellite broadcasting, a service utilizing an MPEG image is recently provided by a network called the Internet having grown with the main object of data communication between computers. In order to ensure the interconnectability of communication in the Internet, the Internet Engineering Task Force (hereinafter abbreviated to IETF) is pushing on standardization. For the standard of an MPEG video transmission format, Request for Comment No. 2038: xe2x80x9cRTP Payload Format for MPEG1/MPEG2 Videoxe2x80x9d (hereinafter abbreviated to RFC 2038) has standardized a transmission method and a packet encapsulation system. It is prescribed by RFC 2038 that the transmission should be made with ES, TS or PS of MPEG utilized as the format of a packet to be transmitted and that in order to prevent the degradation of resolution from being caused by transmission delay, the transmission should be made in accordance with xe2x80x9cRTP: A Transport Protocol for Real-Time Applicationsxe2x80x9d (hereinafter abbreviated to RTP) specified by RFC 1889. It is prescribed that an RTP packet should be stored in a packet based on a user datagram protocol (hereinafter abbreviated to UDP) and this UDP packet should be transmitted by use of the Internet Protocol packet (hereinafter abbreviated to IP packet). With the prior art described above, it is possible to transmit MPEG video data in such a manner that MPEG-TS packets are used in the CATV network while IP packets are used in the Internet.
A system for performing video transmission on the basis of an MPEG-TS system includes a digital satellite broadcasting system and a digital CATV system, as mentioned above. The digital CATV system of those services is a service closely related with an area. Generally, the digital CATV system is constructed with a relatively narrow area taken as a service providing area. Therefore, each CATV business proprietor possesses a CATV center (hereinafter referred to as head end) for delivering programs or contents and an access network for transmitting a video signal so that a ground/satellite broadcasting program received at the head end is retransmitted and/or programs or video contents stored in the head end are transmitted, as required. In such a conventional CATV service, it is required that programs other than broadcast programs should be stored in, for example, VTR or the like and reproduced in accordance with delivering schedule. In a video-on-demand (VOD) service or the like expected as a near-future CATV service, too, it is general that the service is structured in a form in which a digital compression signal of a program is held at a head end in a manner similar to that mentioned above. The video-on-demand service has a problem that a service maintenance cost including the purchase of a rebroadcasting right (or copyright) of video contents in order to hold the video contents, a digital compression processing for the video contents, the storage of compressed or coded video, and so forth is expensive and hence it is not commercially profitable unless the number of times of access to the same contents is made as large as possible. An effective method for solving this problem is such that a plurality of CATV business proprietors hold video contents in cooperation and the contents are utilized through the transmission thereof using a communication network when necessary.
The structuring of such a system has a need to connect the head ends and networks of the plurality of CATV business proprietors by the communication network. In order to connect, for example, a CATV head end in U.S.A. and a set top box (hereinafter abbreviated to STB) in Japan which is a video receiver equipment of a CATV subscriber, it is required that the connection should be made utilizing at least a communication network between U.S.A. and Japan. Under present conditions, however, it is not practical that MPEG-TS being generally utilized in the digital CATV is transmitted as it is. Namely, the video transmission based on MPEG-TS has a problem that a dedicated communication network such as ATM network, satellite network or the like must be used and the charge for communication using this dedicated network is expensive. Also, the dedicated network premises the utilization thereof with a contract point kept in a normally connected condition and hence a great problem is offered in the cost performance aspect in the case where there is used for a service in which the network is occupied in accordance with user""s requests as in the demand-on-service.
An object of the present invention is to enable video transmission based on an MPEG-TS packet without using such a dedicated network.
To solve the above problems, means for connecting a plurality of CATV networks by the Internet is used in the present invention. The Internet is a network ramified over the whole world and has a feature that a dynamic change in connection is possible by using an address applied to an individual client or host computer. Namely, there is no need to fix a connection point beforehand or the connection is effected by use of an address when video transmission is desired. Therefore, free connection setting and low-cost video communication incapable of being realized by the dedicated network are possible. Though the existing Internet has a problem that a transmission band width or the like is narrow, it can easily be foreseen that the insufficiency of band will be eliminated in the near future by ensuring a transmission band by a giga bit router, a resource reservation setup protocol (RSVP) or the like, whereby a global network environment can be realized by the Internet.
A problem arising newly when the CATV networks are connected by use of the Internet, as mentioned above, that is, the problem of a need of the protocol conversion between an MPEG transport protocol used in the CATV network and an IP protocol used in the Internet can be solved by providing an interworking unit for performing the conversion between the MPEG-TS protocol and the Internet protocol. Requirements for a high-speed and low-cost processing in the interworking unit can be met by providing means for improving a packet forming method and a packet conversion method for packets to be transmitted in the MPEG network and the IP network.
More particularly, there are used (1) packet forming means with which the transmission is made with the header of an IP packet stored in a private data region of an adaptation field prescribed in the MPEG-TS system and the interworking unit makes no analysis of private data of the adaptation region or causes the private data to transmit in the Internet with the private data used as the header of the IP packet as it is, and (2) means with which when an MPEG video signal is transmitted from the Internet, the transmission is made with the provision of the condition that an IP packet to be transmitted is restricted in size so that it can be accommodated into a payload without the remainder when the IP packet is divided into MPEG-TS packets.
In this case, the video stream in the MPEG-TS packet is distinguished by a PID value. In the IP packet, on the other hand, the video stream is distinguished by an IP address. Accordingly, when the MPEG-TS packet is to be transferred by use of the IP packet, there is a need to make the conversion between the PID value and the IP address by use of any method.
Another object of the present invention is to solve a problem arising in the case where an IP packet of a video signal transmitted in an IP format is received and the received signal is transmitted in a TS-packetized form. This problem will now be described taking a video transmission system as an example. In a video transmission system utilizing the Internet, video data is transmitted from a video server to a client in an IP format with the data stored in an IP packet. In the case where the transmission/reception is thus made with the IP packet left as it is, the transmission/reception is possible irrespective of the inner data format of the IP packet if the transmitting side and the receiving side recognize the transmission format of data. On the other hand, in the case where there are interconnected a network in which the transmission/reception of a video signal is made in such a TS packet format as prescribed by, for example, the DAVIC (Digital Audio Visual Council) specification (hereinafter, referred to as DAVIC network) or the like and an IP network in which the transmission/reception is made in the IP packet format and access from an STB (Set Top Box) connected to the DAVIC network to a server connected to the IP network is made to receive video data, it is required that video data outputted from the server in an IP packet format should be transmitted to the DAVIC network after the conversion to a TS packet format. In the network using the TS packet, a desired packet is received on the basis of a system in which a packet is broadcast to the network with an address or rather packet identifier (PID) applied to the packet and a client wanting that packet selectively receives that packet in dependence on the PID. Since the TS packet is thus distinguished by the PID value, the following problem arises when IP of an IP packet is terminated for TS packetization. Namely, if there is no correspondence for conversion between an IP address and a PID value, it becomes impossible for an STB on the receiving side to make the judgement of which PID does a TS packet to be received possess.
In other words, the object of the present invention is to provide a method and equipment for conversion between an IP address and a PID value required in the case where IP-packetized video data is received and the received data is retransmitted in a TS-packetized form.
As first means for attaining the above object, the present invention is characterized in that the value of lower 8 bits (Bit: 7-0) of an IP address and the value of lower 8 bits (Bit: 7-0) of a PID value are made the same, and upper 24 bits (Bit: 31-8) of the IP address are degenerated into 5 bits so that the degenerated 5 bits are made to correspond to upper 5 bits (Bit: 12-8) of the PID value. The term of xe2x80x9cdegeneratedxe2x80x9d or xe2x80x9cdegeneracyxe2x80x9d used herein means the conversion of, for example, a 24-bit value into a 5-bit value. In the case where a channel, for example, as described, a frequency for transmission of the TS packet is different, it is possible to set the same degeneracy value (5 bits).
As second means, the present invention is characterized in that the value of lower 8 bits (Bit: 7-0) of an IP address and the value of lower 8 bits (Bit: 7-0) of a PID value are made the same, and upper 24 bits (Bit: 31-8) of the IP address are degenerated into a 5-bit value of 1 to 30 excepting 0 and 31 so that the degenerated 5 bits are made to correspond to upper 5 bits (Bit: 12-8) of the PID value.
As third means, the present invention is characterized in that the value of lower 8 bits (Bit: 7-0) of an IP address and the value of lower 8 bits (Bit: 7-0) of a PID value are made the same, upper 24 bits (Bit: 31-8) of the IP address are degenerated into 3 bits so that the degenerated 3 bits are made to correspond to bits 10 to 8 of the PID value, and bits 12 and 11 of the PID value are made to correspond to 1 and 0, respectively.
As fourth means, the present invention is characterized in that the value of lower 8 bits (Bit: 7-0) of an IP address and the value of lower 8 bits (Bit: 7-0) of a PID value are made the same, upper 24 bits (Bit: 31-8) of the IP address are degenerated into 2 bits so that the degenerated 2 bits are made to correspond to bits 9 to 8 of the PID value, and bits 12 to 10 of the PID value are made to correspond to the category of data transmitted by an IP packet.
As fifth means, the present invention is characterized in that the value of lower 8 bits (Bit: 7-0) of an IP address and the value of lower 8 bits (Bit: 7-0) of a PID value are made the same, upper 24 bits (Bit: 31-8) of the IP address are degenerated into 2 bits so that the degenerated 2 bits are made to correspond to bits 9 to 8 of the PID value, and the conversion into a 3-bit value of 1 to 6 excepting 0 and 7 is made for each category of data transmitted by an IP packet so that the converted 3-bit value is made to correspond to 3 bits including bits 12 to 10 of the PID value.
As sixth means, the present invention is characterized in that a device for receiving IP-packetized video data and retransmitting it after TS-packetization transmits data indicative of the correspondence for conversion between an IP address and a PID value in a form multiplexed with retransmission video data to a video data receiving device.
As seventh means, the present invention is characterized in that data indicative of the correspondence for conversion between an IP address and a PID value generated by the method according to any one of the first to fifth means is transmitted to a video data receiving device each time an IP packet having a different IP address is received and is TS-packetized.
As eighth means, the present invention is characterized in that a retransmitting device transmits data indicative of the correspondence for conversion between an IP address and a PID value generated by the method according to any one of the first to fifth means and data indicative of the correspondence between the IP address and a frequency number for multiplexing of TS packet to a video data receiving device each time an IP packet having a different IP address is received and is TS-packetized.
As ninth means, the present invention is characterized in that a device for receiving IP-packetized video data and retransmitting it after TS-packetization and a device for receiving the TS-packetized and retransmitted video data hold data indicative of the correspondence for conversion between an IP address and a PID value beforehand.
As tenth means, the present invention is characterized in that a device for receiving IP-packetized video data and retransmitting it after TS-packetization and a device for receiving the TS-packetized and retransmitted video data hold data indicative of the correspondence for conversion between an IP address and a PID value generated by the method according to any one of the first to fifth means beforehand.
As eleventh means, the present invention is characterized in that a device for receiving IP-packetized video data and retransmitting it after TS-packetization and a device for receiving the TS-packetized and retransmitted video data hold data indicative of the correspondence for conversion between an IP address and a PID value generated by the method according to any one of the first to fifth means and data indicative of the correspondence between the IP address and a frequency number for multiplexing of TS packet beforehand.
As twelfth means, the present invention is characterized by comprising means with which a device for receiving IP-packetized video data and retransmitting it after TS-packetization and a device for receiving the TS-packetized and retransmitted video data hold data indicative of the correspondence for conversion between an IP address and a PID value generated by the method according to any one of the first to fifth means and data indicative of the correspondence between the IP address and a frequency number for multiplexing of TS packet beforehand, and the retransmitting device can transmits the video data after the IP packet to TS packet conversion on the basis of the data indicative of the correspondence between the IP address and a frequency number for multiplexing of TS packet so that the video data is transmitted to that one of a plurality of connected post-stage transmitting devices which is designated by the data.